1. Field of the Invention
The present invention relates to a semiconductor device, and in particular, to a power semiconductor device comprising a control circuit board.
2. Description of the Related Art
Control circuit boards having electronic components mounted thereon for controlling switching elements are used in semiconductor devices such as intelligent power modules or IPM. Through holes are formed in such a control circuit board having a multi-layer structure, so as to connect the electric patterns of the respective layers. These through holes are, literally, hollow inside. In case where a control circuit board of this type is set in the vicinity of switching elements, noises from the switching elements which are being switched transmit via these through holes and may give an adverse influence on the electronic components mounted on the control circuit board and patterns formed thereon.
Test pads are provided on the control circuit board so as to test the continuity of the control circuit board or to check up an error in the mounting of electronic components after the electronic components have been mounted thereon. As such test pads, for example, circular pads with diameters of 0.5 mm are used. These test pads, however, considerably occupy the space of the control circuit board having a restricted surface area. As a result, it is not avoidable to reduce the ground solids of a pattern on the control circuit board. The reduction of the ground solid pattern also possibly gives an adverse influence on the noise resistance of the electronic components and the pattern on the circuit board.
In this connection, JP-A-08-32240 discloses a technique of filling up the through holes of a multi-layer wiring board, and JP-A-06-69680 discloses a technique of forming through holes having other functions.